The feasibility of using a miniature drive system located exterior to the patient's body to power the Jarvik-7 blood pump was proven in the Phase I effort. The objective of this Phase II effort is to continue the miniaturization of the drive system, and to improve and demonstrate the drive system's capabilities through in-vivo animal testing. Then in Phase III, the miniaturization will be completed, pre-clinical trails with human patients will be performed, and the system will be further improved in preparation for its commercialization. In Phase II, the drive system will be improved for better size, weight, power consumption, battery performance, and control. Six in-vivo tests will be performed, using calves, wherein the Jarvik-7 blood pump will be implanted in the animal and will be powered by the improved miniature external hydraulic drive system. The animal tests will be performed at the Miami Valley Hospital Biosciences Center. The Dayton Cardiovascular-Thoracic Surgery Associates, Inc. will provide surgical expertise for the animal tests. Surgeons and physicians from both organizations will assist in the planning, conduct, analysis and reporting of the in-vivo tests. This Phase II effort will be performed with the assistance of Symbion Inc. and the Department of Artificial Organs of the University of Utah.